At present, flat panel displays have been gradually replacing the bulky CRT displays. The common flat panel displays include liquid crystal displays (LCDs) and organic light emitting diode displays.
In the LCD, each pixel is driven by a corresponding thin film transistor (TFT) on a TFT array substrate and displays image in cooperation with peripheral driving circuits. In the active matrix organic light emission display (AMOLED), each pixel is driven by a corresponding thin film transistor (TFT) on a TFT array substrate and displays image in cooperation with peripheral driving circuits. In the above mentioned displays, the TFT functions as a switching element, and is a key element for achieving image display in the above mentioned displays. The characteristics of the TFT directly determine the development of high performance flat panel displays.
The TFTs that have been industrialized include amorphous silicon TFTs, polysilicon TFTs, monocrystalline silicon TFTs and the like. Among these TFTs, the amorphous silicon TFTs is mostly widely used to manufacture the array substrate of the flat panel display.
Recently, metal oxide TFTs draw more and more attentions. The metal oxide TFTs have the advantage of high carrier mobility so that they can be made very small, and in this case, the resolution of the flat panel display can be increased and the display effect can be improved. Furthermore, the metal oxide TFTs also have such advantages as less occurrence of characteristic unevenness, low cost of materials and processes, low temperature of processes, suitable to a coating process, high transparency, large band gap and the like.
The array substrate comprising the metal oxide TFT is generally manufactured by using six photolithographic processes. If the number of the photolithographic processes can be reduced, that is, if the number of the masks used in the manufacturing process can be reduced, it is possible to increase the production efficiency and reduce the production cost.